I've written about the alleged chemical attack in Saraqeb in the past, and one new element of the story the BBC report covers is another item dropped from a helicopter during the attack

One device was said to have landed on the outskirts of Saraqeb, with eyewitnesses describing a box-like container, with a hollow concrete casing inside.
In another video, a rebel fighter holds a canister said to be hidden inside the devices. Witnesses claim there were two in each container.
Another video shows parts of a canister on the ground, surrounded by white powder.

I've been able to acquire a video showing the remains of the "box-like container" described in the report, along with the white power.

While this doesn't look like much it's interesting to note children are happy to walk within a few feet of the white powder without any apparent ill effect, which suggests it might not be a lethal chemical agent.